Alimentary immune function Flashcards
What is the surface area of the GI tract?
400m^2
What is the dual immunological role of the GI?
Must maintain tolerance to food antigens and commensal bacteria and an active immune response for pathogens. It is therefore in a constant state of ‘restrained activation’.
What immunological purpose does the microbiota have?
require it for development of healthy immune system
How many microbes in gut?
10^14
state 4 major phyla of microbiota
Bacteriodetes, firmicutes, Actinobacteria, proteobacteria.
Where are microbiota most abundant?
Colon, where there are no host digestive factors (e.g. enzymes, gastric acid…).
3 types of microbiota? Dynamics between the three?
SYMBIONTS: take up energy, but provide help and regulation; COMMENSALS: function not known but prevent pathogens binding to epithelium and outcompete; PATHOBIONTS capable of causing inflammation. ………………………….. These are in balance - called immunological equilibrium.
What is the name when microbiota classes are disturbed?
Dysbiosis, altered numbers of pathobionts caused by an immunological event e.g. pathogen invasion –> leads to inflammation.
What are causes of dysbiosis? (x5)
Infection, diet, xenobiotics, hygiene and genetics, as well as infection or even diet.
What is issue with dysbiosis?
Can result in large amounts of bacterial metabolites and toxins produced: this can have far reaching effects, and result in systemic diseases of the adipose, liver, lung and even brain.
What are physical barriers against infection. (x2 (x3))
PHYSICAL ANATOMICAL BARRIERS: Epithelial barrier with tight junctions, mucous layer, paneth cells of small intestine (bases of crypts of Lieberkuhn secrete antimicrobial peptides and lysozyme.
PHYSICAL CHEMICAL BARRIER: pH in stomach, enzymes.
What is the second “line of defence/barrier” against infection
Commensal bacteria
What form of defence does the tract have incase of breach by bacteria?
MALT (Mucosa associated lymphoid tissue) and GALT (Gut) which are immunoogical.
Where and what are MALT found?
In the submucosa (below the epithelium) as lymphoid mass containing lymphoid follicles.
Follicles are surrounded by HEV post-capillary venules, allowing for easy passage of lymphocytes.
Some found in mouth eg pharengeal tonsils
Where is GALT found and what types are there (x2)? IMMUNOLIGCAL FUNCTION?
Responsible for adaptive AND innate immune responses.
Found in organised and non-organised forms.
Non-organised: Intra-epithelial lymphocytes – Make up one-fifth of intestinal epithelium, e.g., T cells, NK cells Lamina propria lymphocytes
Organised: Peyer’s patches (small intestine) Caecal patches (large intestine) Isolated lymphoid follicles Mesenteric lymph nodes (encapsulated).
What is the structure of Peyer’s Patches?
Found in small intestine – mainly distal ileum.
- Aggregated lymphoid follicles covered with follicle associated epithelium (FAE).
- Organised collection of naïve T cells and B-cells.
- Associated with M (microfold) cells which are found within FAE.
What is the function of Peyer’s patches? How do M cells perform their function?
Development requires exposure to bacterial microbiota (50 in last trimester foetus, 250 by teens).
- Antigen uptake via M (microfold) cells within FAE.
- M cells therefore sample antigens. M cells then present these antigens to the patches and activate them.
- M cell transfers bacteria for phagocytosis in patches.
HOW DO M-CELLS TRANSFER? M cells express IgA receptors, facilitating transfer of IgA-bacteria complex into the peyer’s patches.
What is FAE?
Epithelium covering mucosa-associated lymphoid tissue (MALT).
What is lamina propria?
Thinlayer of connective tissue that forms part of the moist linings known as mucous membranes or mucosa, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital tract.
This is where lymphocytes migrate in circumstances of infection. Antibodies are then secreted into the lumen of the GIT from the lamina propria.
What are trans-epithelial dendritic cells?
An example of trans-epithelial antigen sampling in the gut. Have long extensions which penetrate through the epithelium and samples antigens. They bring antigens back and transfer them to mysenteric lymph nodes.
Describe pathway of secretory IgA formation.
Plasma cells produce dimer IgA which bind to to Poly-Ig receptor on basolateral membrane.
The dimer-receptor complex is endocytosed and cleaved to liberate the receptor so that it can be returned to the membrane.
Then, Iga has secretory component attached which provides protection for the antibody against harsh environment of the gut .
A secretory dimer is then released into the gut.
WHAT IS THE PURPOSE OF sIgA?
Bind to luminal antigens and prevent adhesion to epithelial lining and thereby protecting against invasion. This is known as protection through NEUTRALISATION.
